In 2014, based on similarities of the orbits of a group of recently discovered extreme trans-Neptunian objects, astronomers hypothesized the existence of a super-Earth planet, 2 to 15 times the mass of the Earth and beyond 200 AU with possibly a high inclined orbit at some 1500 AU. In 2016 further work showed this unknown distant planet is likely on an inclined, eccentric orbit that goes no closer than about 200 AU and no further than about 1600 AU from the Sun. The orbit is predicted to be anti-aligned to the clustered extreme trans-Neptunian objects. Because Pluto is no longer considered a planet by the International Astronomical Union, this new hypothetical object has become known as Planet Nine.

The name "Nibiru" is derived from the works of the ancient astronaut writer Zecharia Sitchin and his interpretations of Babylonian and Sumerian mythology. According to Sitchin's interpretation of Babylonian religious texts, which contradicts conclusions reached by credited scholars on the subject, a giant planet (called Nibiru or Marduk) passes by Earth every 3,600 years and allows its sentient inhabitants to interact with humanity. These beings, which Sitchin identified with the Anunnaki of Sumerian myth, would become humanity's first gods.